1. Field of the Invention
The present invention relates to a fuel cell system equipped with fuel cells capable of generating electrical energy by electrochemical reaction of combining hydrogen and oxygen, and suitably applicable to movable bodies such as automotive vehicles, electric vehicles, marine vessels, and other mobile devices equipped with a refrigeration cycle for use of air conditioning and the like.
2. Description of the Related Art
In a fuel cell vehicle equipped with a fuel cell system composed of a fuel cell stack to be used as vehicle's driving power, the temperature of a cooling water for use of the fuel cell system is approximately 80° C., and which is lower than the temperature of a cooling water (approximate 100° C.) for use of cooling an internal combustion engine mounted on the vehicle. There is accordingly a possibility of not always providing an adequate heating performance of the air conditioning when only the cooling water for the fuel cell system is used for heating the air in the compartment of the vehicle.
There are many conventional techniques using a refrigeration cycle (or a heat pump) as a power source for heating the compartment of a vehicle. Japanese patent Kohyo (Japan unexamined national publication of translated version for PCT/DE2002/003876) No. JP 2005-511373 has disclosed one of those conventional techniques.
In general, because super-charged air (oxidizing gas) of a high temperature is supplied to a fuel cell stack in a fuel cell system, waste heat of exhaust air discharged from the fuel cell stack is circulated and returned to a refrigeration cycle in the fuel cell system. However, because the exhaust air contains a lot of water component, the water component contained in the exhaust air becomes frozen when the temperature of a refrigerant flowing through the refrigeration cycle becomes not more than its freezing point. This phenomenon decreases heat exchanger effectiveness in the fuel cell system. In the worst case, a pipe through which the exhaust air flows is plugged or blocked by the frozen water. At last, the fuel cell system thereby stops.